1. Field of the Invention
This invention relates to a bar matrix for the fastening of a dental prosthetic supra-construction on a bar projection.
2. Discussion of Related Art
Bar matrices are part of a bar attachment, with which part prosthesis or total prosthesis are held in the lower jaw or upper jaw, in an implant-retained manner. Such bar attachments have a bar projection and a bar matrix. The bar projection is a fine-mechanical anchoring element, which includes a crosspiece which runs between implants and orally blocks these with one another. The complete crosspiece with the fastener for fastening on the implants is called a bar projection.
A bar matrix is integrated into the removable part of the tooth prosthesis. The bar matrix, often also called bar rider, has a sleeve with suitable retention elements, in order to effect an anchoring in the dental-prosthetic supra-construction.
With modern supra-constructions, a metallic support construction should be present, on which the actual supra-construction of plastic is held. The support construction is called the cast model. The cast model includes openings for connecting the cast model to the plastic construction, which are indicated as so-called polymerization windows.
While the development, which is often made by dentists, has concerned itself primarily with the releasable connection between the bar matrix and the bar projection, the problem of the anchoring of the bar matrix in the dental-prosthetic supra-construction has been neglected, because this problem essentially occurs only in dental laboratories, which concern the manufacture of the dental-prosthetic supra-construction. Indeed, on manufacture of the dental-prosthetic supra-construction, it has been found that the retention elements are capable of accommodating only an insufficient retention force on the sleeve of the bar matrix, because the retention elements could only be kept extremely small on account of the design. The constructions of the bar matrices common today envisage a sleeve which is at least approximately u-shaped in cross section and which practically along the apex line in each case has a longitudinal surface running buccally and lingually, the longitudinal surfaces having a maximal extension in the lingual and buccal direction, so that they do not exceed the sleeve width. This is necessary, because otherwise the wall thickness of the dental-prosthetic supra-construction or of the tooth construction would be too thin-walled or would project outward.
The bar attachment is a development by Dr. Hans Dolder that represents a solution for holding dental prosthesis which are supported not only in a purely gingival manner. As mentioned, this Dolder bar has been proven over many years. A further development of this Dolder bar is shown for example in European Patent Reference EP 1 192 916, with which the fastening of the matrix onto the projection functioning as a bar, does not function with a resilient mechanical retention, but with a permanent magnet in a shape to the bar, and is surrounded by a sleeve. With this solution, the retention elements are integrally formed in a lingual and buccal manner and form the shape of an elongate, laterally integrally formed lug. Here, the anchoring of the dental-prosthetic supra-construction is only rudimentarily realized.
A bar matrix is known from German Patent Reference DE-3009758A, which is a sleeve with pins which are integrally formed thereon and running in the occlusal direction. The retention forces which may be achieved with these are minimal.
In contrast, the conventional solution according to German Patent Reference DE-29609304 U, with which the bar matrix is formed as a sleeve with wings which are integrally formed in a buccal and lingual manner.
A bar projection which is practically integrally formed on the patient, and with which accordingly also the bar matrix which is formed as a U-shaped sleeve rectangular in cross section, and the matrix and projection are molded to one another, is completely unusual. The solution according to U.S. Patent Application Publication US-2003/0211 444 may thus not be combined with a Dolder bar.
Finally, a bar matrix is known from U.S. Pat. No. 4,209,904, which is formed from a number of riders which may be placed on the Dolder bar, wherein the riders have a sleeve section, on which a tab bent in the occlusal direction is integrally formed. The solution is only suitable for supra-constructions without a cast model, thus without metal reinforcement. If the tabs are located at a location where the pallatinal surface of the teeth runs very close to the bar, then the retention tabs must be ground away, and the retention is greatly weakened.